Winter Trees and Shrubs: Northern Catalpa

The names of plants often contain clues that can either help with identification or that tell something about the plant’s history or use. The name, catalpa, is said to be derived from the Muscogee word, katałpa, meaning “winged head,” presumably referring to the tree’s winged seeds. Or maybe, as one writer speculates, it refers to the large, heart-shaped, floppy leaves that can make it look like the tree is “ready to take flight.” Or perhaps it’s a reference to the fluted, fused petals of the tree’s large, tubular flowers. I suppose it could mean any number of things, but I’m sticking with its seeds, which are packed by the dozens in the tree’s long, slender, bean-like fruits. The seeds are flat, pale brown, and equipped with paper thin, fringed appendages on either side that assist in wind dispersal – wings, in other words.

winged seeds of northern catalpa (Catalpa speciosa)

Catalpa speciosa, or northern catalpa, is a relatively fast growing, short-lived tree native to the Midwest and one of only two species in the genus Catalpa found in the United States. Its distribution prior to the arrival of Europeans appears to have been restricted to a portion of the central Mississippi River valley, extending west into Arkansas, east into Tennessee, and north into Illinois and Indiana. It has since been widely planted outside of its native range, naturalizing in areas across the Midwest and eastern US. Early colonizers planted northern catalpa for use as fence posts, railroad ties, and firewood. Its popularity as an ornamental tree is not what it once was a century ago, but it is still occasionally planted in urban areas as a shade tree. Its messiness – littering the ground below with large leaves, flowers, and seed capsules – and its tendency to spread outside of cultivation into natural areas are reasons why it has fallen out of favor with some people.

The oval to heart-shaped, 8 to 12 inch long leaves with long petioles rotting on the ground below the tree are one sure sign that you’ve encountered a catalpa in the winter time. The leaves are some of the first to fall at the end of the growing season, briefly turning an unmemorable yellow before dropping.

leaf of northern catalpa (Catalpa speciosa) in the winter with soft hairs on the underside still visible

The leaf arrangement on northern catalpa is whorled and sometimes opposite. The twigs are easy to identify due to several unique features. They are stout, round, and grayish brown with prominent lenticels. The leaf scars are large, rounded, and raised up on the twig, looking a bit like little suction cups. They are arranged in whorls of three, with one scar considerably smaller than the other two. A series of bundle traces inside the scar form an ellipse. The leaf buds are tiny compared to the scar and are protected by loose, pointed, brown bud scales. Northern catalpa twigs lack a terminal bud. In the winter, seed capsules or the stalk of an old inflorescence often remain attached to the terminal end of the twig. The pith inside of the twig is thick, white, and solid.

twig of northern catalpa (Catalpa speciosa)

pith inside twig of northern catalpa (Catalpa speciosa)

Another common name for Catalpa speciosa is cigar tree, a name that comes from its up to 18 inch long, cigar-like seed capsules that hang from the otherwise naked tree throughout the winter. The sturdy, cylindrical pod starts out green in the summer and turns dark brown by late fall. Seed pods that haven’t fallen or already split open will dehisce in the spring time, releasing their papery seeds to the wind.

fruits of northern catalpa (Catalpa speciosa) hanging from the tree in the winter

The young bark of northern catalpa is thin and easily damaged. As it matures, it becomes furrowed with either scaly ridges or blocky plates. Mature trees are generally twisted at the base but otherwise grow straight, reaching 30 to 60 feet tall (sometimes taller) with an open-rounded to narrow-oval crown.

maturing bark of northern catalpa (Catalpa speciosa)

Northern catalpa is one of the last trees to leaf out in the spring. In late spring or early summer, 10 inch long clusters of white, tubular flowers are produced at the tips of stems. Before the flowers open, they look a bit like popped popcorn, reminding me of a song from my childhood (which I will reluctantly leave right here). The margins of its trumpet-shaped petals are ruffled and there is yellow, orange, and/or purple spotting or streaking on the inside of the tubes.

flower of northern catalpa (Catalpa speciosa) just before it opens

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Winter Trees and Shrubs: Netleaf Hackberry

Boise, Idaho is frequently referred to as the City of Trees despite being located in a semiarid region of the Intermountain West known as the sagebrush steppe where few trees naturally grow. It earns this moniker partly because the name Boise is derived from the river that runs through it (the Boise River), which was named La Rivere Boisse, or The Wooded River, by early French trappers. Although it flows through a largely treeless landscape, The Wooded River was an apt name on account of the wide expanse of cottonwoods and willows that grew along its banks. The fervent efforts of early colonizers to plant trees in large numbers across their new city also helped Boise earn the title, City of Trees. Today, residents continue the legacy of planting trees, ensuring that the city will remain wooded for decades to come.

As is likely the case for most urban areas, the majority of trees being planted in Boise are not native to the region. After all, very few tree species are. However, apart from the trees that flank the Boise River, there is one tree in particular that naturally occurs in the area. Celtis reticulata, commonly known as netleaf hackberry, can be found scattered across the Boise Foothills amongst shrubs, bunchgrasses, and wildflowers, taking advantage of deep pockets of moisture found in rocky outcrops and draws.

The western edge of netleaf hackberry’s range extends to the northwest of Boise into Washington, west into Oregon, and down into California. The majority of its range is found south of Idaho, across the Southwest and into northern Mexico, then east into the prairie regions of Kansas and Oklahoma. Previously placed in the elm family, it is now considered a member of the family Cannabaceae (along with hemp and hops). It’s a relatively small, broad tree (sometimes a shrub) with a semi-rounded crown. It grows slowly, is long-lived, and generally has a gnarled, hardened, twisted look to it. It’s a tough tree that has clearly been through a lot.

The leaves of Celtis reticulata are rough, leathery, and oval to lance shaped with serrate or entire leaf margins. Their undersides have a distinct net-like pattern that gives the tree its common name. A very small insect called a hackberry psyllid lays its eggs inside the leaf buds of netleaf hackberries in the spring. Its larvae develop inside the leaf, feeding on the sugars produced during photosynthesis, and causing nipple galls to form in the leaves. It’s not uncommon to see a netleaf hackberry with warty-looking galls on just about every leaf. Luckily, the tree doesn’t seem to be bothered by this.

fallen leaves of netleaf hackberry (Celtis reticulata) with nipple galls

The fruit of netleaf hackberry is a pea-sized drupe that hangs at the end of a pedicel that is 1/4 to 1/2 inch long. Its skin is red-orange to purple-brown, and its flesh is thin with a large seed in the center. The fruits, along with a few random leaves, persist on the tree throughout the winter and provide food for dozens of species of birds and a variety of mammals.

persistent fruit of netleaf hackberry (Celtis reticulata)

Celtis reticulata is alternately branched. Its twigs are slender, zig-zagging, and often curved back towards the trunk. They are reddish-brown with several pale lenticels and have sparse, fine, short hairs that are hard to see without a hand lens. The leaf scars are small, half-round, and raised up from the twig. They have three bundle scars that form a triangle. The buds are triangle-shaped with fuzzy bud scales that are slightly lighter in color than the twig. The twigs are topped with a subterminal bud, and the pith (the inner portion of the twig) is either chambered or diaphragmed and difficult to see clearly without a hand lens. 

twigs of netleaf hackberry (Celtis reticulata)

The young bark of netleaf hackberry is generally smooth and grey, developing shallow, orange-tinged furrows as it gets older. Mature bark is warty like its cousin, Celtis occidentals, and develops thick, grey, corky ridges. Due to its slow growth, the bark can be retained long enough that it becomes habitat for extensive lichen colonies.

bark of young netleaf hackberry (Celtis reticulata)

bark of mature netleaf hackberry (Celtis reticulata)

Netleaf hackberry is one of the last trees to leaf out in the spring, presumably preserving as much moisture as possible as it prepares to enter another scorching hot, bone-dry summer typical of the western states. Its flowers open around the same time and are miniscule and without petals. Their oversized mustache-shaped, fuzzy, white stigmas provide some entertainment for those of us who take the time to lean in for a closer look.

spring flowers of netleaf hackberry (Celtis reticulata)

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Photos of netleaf hackberry taken at Idaho Botanical Garden in Boise, Idaho.

Winter Trees and Shrubs: Eastern Redbud

Botanizing doesn’t have to end when the leaves fall off the trees and the ground goes frozen. Plants may stop actively growing during this time, but they are still there. Some die back to the soil level and spend the entire winter underground, leaving behind brown, brittle shells of their former selves. Others, particularly those with woody stems, maintain their form (although many of them leafless) as they bide their time while daylength dips and rises again, bringing with it the promise of warmer weather. Plants that leave us with something to look at during the winter can still be identified. Without foliage or flowers to offer us clues, we rely instead on branches, bark, and buds to identify woody species. In some cases, such features may even be more helpful in determining a certain species than their flowers and foliage ever were. Either way, it’s a fun challenge and one worth accepting if you’re willing to brave the cold, hand lens and field guides in tow.

In this series of posts I’ll be looking closely at woody plants in winter, examining the twigs, buds, bark, and any other features I come across that can help us identify them. Species by species, I will learn the ropes of winter plant identification and then pass my findings along to you. We’ll begin with Cercis canadensis, an understory tree commonly known as eastern redbud.

Eastern redbud is distributed across central and eastern North America, south of southern Michigan and into central Mexico. It is also commonly grown as an ornamental tree outside of its native range, and a number of cultivars have been developed for this purpose. Mature trees reach up to 30 feet and have short trunks with wide, rounded crowns. Its leaves are entire, round or heart-shaped, and turn golden-yellow in the fall. Gathered below the tree in winter, the leaves maintain their shape and are a light orange-brown color.

fallen leaf of eastern redbud (Cercis canadensis)

Eastern redbud is alternately branched with slender, zig-zagging twigs that are dark reddish-brown scattered with several tiny, light-colored lenticels. Older sections of branches are more grey in color. Leaf scars (the marks left on twigs after leaves fall) are a rounded triangle shape and slightly raised with thin ridges along each side. The top edge of the leaf scar is fringed, which I found impossible to see without magnification. Leaf buds are egg-shaped and 2-3 mm in length with wine-red bud scales that are glabrous (smooth) with slightly white, ciliate margins. Descriptions say there are actually two buds – one stalked and one sessile. If the second bud is there, it’s miniscule and obscured by the leaf scar. I haven’t actually been able to see one. Twigs lack a terminal bud or have a tiny subterminal bud that points off to one side. The pith of the twigs is rounded and pale pink. Use sharp pruners or a razor blade to cut the twig in half lengthwise to see it.

twig and buds of eastern redbud (Cercis canadensis)

Bark is helpful in identifying woody plants any time of year, but is especially worth looking at during the winter when branches have gone bare. The bark of young eastern redbud is grey with orange, furrowed streaks running lengthwise along the trunk. In mature trees, the bark is gray, scaly, and peels to reveal reddish-brown below.

bark of young eastern redbud (Cercis canadensis)

bark of mature eastern redbud (Cercis canadensis)

Eastern redbud is in the bean family (Fabaceae) and its flowers and fruits are characteristic of plants in this family. Fruits can persist on the tree throughout the winter and are another way to identify the tree during the off-season. Seed pods are flat, dark red- or orange-brown, and up to 2.5 inches long with four to ten seeds inside. The seeds are flat, round, about 5 millimeters long, and ranging in color from orange-brown to black.

persistent fruits of eastern redbud (Cercis canadensis)

seeds of eastern redbud (Cercis canadensis)

Eastern redbud flowers in early spring before it has leafed out. Clusters of bright pink flowers form on old branches rather than new stems and twigs. Sometimes flowers even burst right out of the main trunk. This unique trait is called cauliflory.

cauliflory on eastern redbud (Cercis canadensis)

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Photos of eastern redbud taken at Idaho Botanical Garden in Boise, Idaho.

Field Trip: Bergius Botanic Garden and Copenhagen Botanical Garden

There are very few downsides to working at a botanical garden, but one of them is that the growing season can be so busy that taking time off to visit other botanical gardens when they are at their peak is challenging. Case in point, my visit to Alaska Botanical Garden last October. Another case in point, this December’s visit to a couple of gardens in Scandinavia.

That’s right, Sierra and I took a long (and much needed) break from work and headed to the other side of the world for some fun in the occasional sun of Denmark and Sweden. While we were there we visited two botanical gardens, one in Stockholm and the other in Copenhagen. Considering we were there in December, we were impressed by how many things we found all around that were still blooming. We were also impressed by how much winter interest there was in the form of seed heads, spent flower stalks, and other plant parts left in place, as opposed to everything being chopped down to the ground as soon as fall arrives (which is often the case in our part of the world). We may not have been there in the warmest or sunniest time of year, but there was still plenty of natural beauty to capture our attention.

Bergius Botanic Garden

The first of the two gardens we visited was Bergius Botanic Garden (a.k.a. Bergianska trädgården) in Stockholm, Sweden. It is located near Stockholm University and the Swedish Museum of Natural History. It was founded in 1791 and moved to its current location in 1885. It was immediately obvious that the gardens were thoughtfully planned out, particularly the systematic beds in which the plants were organized according to their evolutionary relationship to each other. The extensive rock garden, which was a collection of small “mountains” with a series of paths winding throughout, was also impressive. Since we arrived just as the sun was beginning to set, we were happy to find that the Edvard Anderson Conservatory was open where we could explore a whole other world of plants, many more of which were flowering at the time.

Walking into Bergius Botanic Garden with the Edvard Anderson Conservatory in the distance.

Sierra poses with kale, collard, and Brussels sprout trees in the Vegetable Garden.

seed heads of velvetleaf (Abutilon theophrasti)

corky bark of cork-barked elm (Ulmus minor ‘Suberosa’)

pomelo (Citrus maxima) in the Edvard Anderson Conservatory

Camellia japonica ‘Roger Hall’ in the Edvard Anderson Conservatory

carrion-flower (Orbea variegata) in the Edvard Anderson Conservatory

Cape African-queen (Anisodontea capensis) in the Edvard Anderson Conservatory

Copenhgen Botanical Garden

The Copenhagen Botanical Garden (a.k.a. Botanisk have) is a 10 hectare garden that was founded in 1600 and moved to its current location in 1870. It is part of the University of Copenhagen and is located among a series of glasshouses built in 1874, a natural history museum, and a geological museum. Unfortunately, the glasshouses and museums were closed the day we visited, but we still enjoyed walking through the grounds and exploring the various gardens.

A large rock garden, similar to the one at Bergius, was a prominent feature. We learned from talking to a gardener working there that since Denmark is not known for its rich supply of large rocks, most of the rocks in the garden came from Norway. However, a section of the rock garden was built using fossilized coral found in Denmark that dates back to the time that the region was underwater.

Another great feature was the Nordic Beer Garden, a meticulously organized collection of plants used in beer recipes from the time of the Vikings to the Nordic brewers of today. Even though the majority of the plants in this garden were dormant, the interpretive signage and fastidious layout was memorable.

Walking into Copenhagen Botanical Garden with the Palm House in the distance.

lots of little pots of dormant bulbs

seed head of Chinese licorice (Glycyrrhiza echinata)

fruits of Chinese lantern (Physalis alkekengi)

alpine rose (Rhododendron ferrugineum)

Viburnum farreri ‘Nanum’

seed head of rose of Sharon (Hibiscus syriacus)

pods exposing the seeds of stinking iris (Iris foetidissima)